If they made them light with no other compromise, I think the point would be moot, but firstly the lack of a 76 makes regular non-arranger use a bit more difficult if you use a one keyboard rig. The fact that these keyboards include SMF and MP3 players seems to indicate there is quite a demand for non-arranger usage (before the 'it's perfectly fine for ordinary arranger use' camp jumps in, here), and the greater the number of keys, the more flexible your setups can be (ever tried TWO splits on a 61?).
The T2's keyboard, although a little light for me, at least IS built to workstation standards, but it is galling to have to pay $2000 MORE just for a decent keyboard (and little else since the S900 came out), when the Yamaha WS line (Motifs) has the same keyboard on it's LOWEST level offering.
I guess for many of us, we simply expect the same build quality from arrangers as we get for equivalent cost workstations. If Yamaha can make a WS product at that price, built to THAT standard, why not an arranger? There is little extra in the weight of the 61 (about 30 lbs. total), certainly not enough to put MANY users off it) and anyone who has played one will comment about how solid and well built it is compared to the arranger line.
And PLEASE don't tell me about the needs of the WS users for a more roadworthy product. You can't have it BOTH ways. Either the PSR and Tyros2 ends up in basically the same hands as the Motifs. I would be prepared to say that nearly the same percentage of Motifs end up in homes and studios as does arrangers. Plenty of pros using Yamaha arrangers, despite their build quality (they HAVE to, if they want the features and sounds), and plenty of home users buying Motifs.
So why the apparent freebie (or close to it) of a decent build quality for the WS users, and close to toy-like construction for even the TOTL Yammie arranger? SOMEONE is getting shafted... Is it us (the arranger user), or is the WS user, who has to lug around a tad more weight?
I know how I feel...
An arranger is just a tool. What matters is what you build with it..!